930 MINNESOTA BOTANICAL, STUDIES. 



narcotize or paralyze spiders, crickets or caterpillars by sting- 

 ing, thus rendering them motionless. In this condition they 

 are sealed into the wasp's nest containing the egg, in order to 

 serve as food for the young wasp. This condition becomes 

 more complicated by the intrusion of another wasp which un- 

 observed lays its egg in the nest already supplied with the 

 necessary food. The foreign egg develops first and the young 

 wasp not only eats the food supplied by its foster mother, but 

 also the egg. From these conditions to true parasitism is only 

 a step. Some wasps lay their eggs directly into the tissues 

 of the caterpillar. The egg develops and the young larva 

 feeds upon the less vital tissues of the host so as to prolong 

 life as much as possible. Finally only the outer tegument of 

 the host remains which is utilized as a protective covering 

 during the resting stage. 



We may also mention the phenomena induced by grafting. 

 These are usually not designated as symbioses'though they 

 evidently partake of that nature. It is true graft and stock do 

 not form an association of two complete individuals, yet in 

 their functional relationships they form a most perfect sym- 

 biosis (mutualism). 



These examples will suffice to make clear how difficult it is 

 in many instances to recognize phenomena of undoubted sym- 

 biosis. 



RECOGNIZED PHENOMENA OF SYMBIOSIS. 



The phenomena of symbiosis here defined have been more or 

 less discussed by scientists and have received recognition. 

 Authors are, however, at variance as to their exact limitations 

 which makes the definitions subjectively variable. The phen- 

 omena of symbiosis may be classified as follows: 



I. Incipient Symbiosis (Indifferent Symbiosis). 



1. Accidental Symbiosis. 



2. Contingent Symbiosis (Raumparasitismus). 



II. Antagonistic Symbiosis. 



1. Mutual Antagonistic Symbiosis (Mutual Parasitism). 



2. Antagonistic Symbiosis (Parasitism). 



a. Obligative Antagonistic Symbiosis. 



b. Facultative Antagonistic Symbiosis. 



3. Saprophytism. 



a. Facultative Saprophytism. 



b. Obligative Saprophytism. 



